Method and apparatus for replacing a failed channel unit of a sectored base station, in a cellular radio system, with an additional channel unit

ABSTRACT

A method for securing the operation of a base station having a radio coverage area divided into at least two sectors, and a base station having antennas, with combiners and branching units, and at least one channel unit for each sector, which allow the base station to establish a radio connection with active radio transceivers currently located in the base station sectors. In the method, the base station is provided with an additional channel unit the traffic capacity of which is selectably switchable to one of the base station sectors. To secure the operation of the base station when one of the channel units fails, the operation of the channel units of the base station is monitored. When one of the channel units fails, the additional channel unit is connected to the antenna of the sector of the failed channel unit by a switch, which connects the antenna attachments of the additional channel unit to the antenna of one sector at a time.

This application claims benefit of international applicationPCT/Fl94/00424 filed Sep. 22, 1994.

TECHNICAL FIELD

The invention relates to a method for securing the operation of a basestation having a radio coverage area divided into at least two sectors,the base station comprising antenna means and at least one channel unitfor each sector, which allow the base station to establish a radioconnection with active radio transceivers currently located in thesectors of the base station, wherein the base station is provided withan additional channel unit the traffic capacity of which is selectablyswitchable to one of the base station sectors. The invention alsorelates to a base station in a radio system, the radio coverage area ofthe base station being divided into at least two sectors and the basestation comprising antenna means and at least one channel unit for eachsector, which allow the base station to establish a radio connectionwith active radio transceivers currently located in the sectors of thebase station, the base station further comprising an additional channelunit the traffic capacity of which is selectably switchable to one ofthe base station sectors.

As used herein, the term antenna means refers not only to the antennarequired for transmission and reception but also to the means thatconnect the antenna attachments of a channel unit to the antenna of thebase station. Such means include a combiner means, which combinessignals transmitted by channel units intended to be used in the samesector before they are applied to the antenna, and a branching means,which filters and amplifies signals received by the antenna of aspecific sector and branches them to the receivers of different channelunits.

TECHNICAL BACKGROUND ART

Finnish Patent Application 911 199 discloses a solution where anadditional channel unit is connected to a sectored base station in acellular radio system. The additional channel unit can be connected to asector that instantaneously needs additional capacity. In this solution,the additional channel unit is connected so that its transmitter can beswitched by a relay switch to a combiner means belonging to the antennameans of the selected sector. On the contrary, the reception side of theadditional channel unit is implemented such that signals received fromdifferent sectors are combined by a combiner means and applied to thereceiver of the additional channel unit. Accordingly, signals receivedfrom each sector of the base station are thus continually applied to thereceiver of the additional channel unit.

The solution according to Finnish Patent Application 911 199, wheresignals from each sector of the base station are applied continually tothe additional channel unit, has several drawbacks, the most severebeing:

complicated cabling;

susceptibility to interference when the fixed channel unit of one of thesectors fails in such a way that the antenna attachment of the receiverof the failed channel unit forwards signals interfering with the otherchannel units of the base station; this interference may render all ofthe receivers of the base station inoperative, as the receiver of thefailed channel unit is still connected to the other receivers of thebase station through the combiner means of the reception side;

susceptibility to interference during normal traffic operation due tothe fact that the additional channel unit is permanently connected toall of the sectors of the base station so that it also gathersinterferences and background noise from within all sectors. In the worstcase, it may happen that a signal received by the receiver of theadditional channel unit from a cell of another mobile radio networkcovers a desired signal or at least substantially deteriorates thequality of the connection (the solution does not follow the frequencyre-use scheme that has been made specifically for each sector);

greater attenuation due to the summing of signals on the reception side,which causes a greater attenuation on the signal path, so that thesensitivity of the receivers is impaired.

SUMMARY OF THE INVENTION

The object of the present invention is to avoid the above problems andto provide a method by means of which a failed channel unit of asectored base station in a cellular radio system can be replaced with anadditional channel unit, and which ensures that the failed channel unitwill not interfere with the operation of the other channel units of thebase station when the antenna attachment of the failed channel unitforwards signals at a frequency such that they would otherwise interferewith the operation of the base station. These objects are achieved by amethod according to the invention, which is characterized by monitoringthe operation of the channel units of the base station; and switching,when one of the channel units fails, the additional channel unit to theantenna means of the sector of the failed channel unit by a switchingmeans which connects the antenna attachments of the additional channelunit to the antenna means of one sector at a time.

The invention also relates to a base station where the method accordingto the invention can be applied. The base station according to theinvention is characterized in that the additional channel unit isswitched to the antenna means of a selected sector by a switching means,which connects the antenna attachments of the additional channel unit tothe antenna means of one sector at a time.

The invention is based on the idea that the operation of a sectored basestation can be secured more efficiently and reliably than previouslywhen one of the channel units fitted in the base station fails byproviding an additional channel unit in the base station. The antennaattachments of the additional channel unit can be switched to one of theantennas of the base station by a relay-type switch. This switchingensures that the failed channel unit will not interfere with the otherreceivers at the base station due to signals possibly propagatingthrough its antenna attachments. The most important advantage of themethod and the base station according to the invention is thus that theyminimize the disadvantage caused by the failure of a channel unit. Atbest, the failed channel unit can be replaced with the additionalchannel unit, whereby normal traffic operation can be continuedimmediately even in the sector of the failed channel unit. Not even inthe worst case is the failure able to interfere with traffic takingplace in the other sectors.

Another major advantage of the method and the base station according tothe invention is that a single switching means, i.e. a relay-typeswitch, is needed for the switching which replaces the failed channelunit with the additional channel unit. The solution according to theinvention is thus simpler and cheaper than the prior art solutions.

Other advantages of the method and the base station according to theinvention over the prior art include simple cabling, lower level ofbackground noise in reception, excellent sensitivity of reception, andthe possibility to utilize the additional channel unit while followingthe sector-specific frequency re-use scheme.

BRIEF DESCRIPTION OF THE DRAWING

In the following, the invention will be described more fully by means ofa preferred embodiment with reference to the attached FIGURE, whichshows a preferred embodiment of a base station according to theinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The FIGURE shows a sectored GSM base station the coverage area of whichis divided into three sectors. The structure and operation of the GSMsystem are described e.g. in The GSM System for Mobile Communications,M. Mouly & M-B Pautet, Palaiseau, France, 1992, ISBN: 2-9507190-0-7,wherefore they will not be described more closely herein.

The base station 13 shown in the FIGURE comprises a fixed channel unit(TRX) 1, 2 and 3, and an antenna 4, 5 and 6 for each sector of the basestation, respectively, whereby the base station is able to establish aradio connection with active radio transceivers located in the sectors.The transceivers 1, 2 and 3 are connected to the antennas 4, 5 and 6 bycombiner means 7 and branching means 8. If required, more than onechannel unit can be connected to each antenna, while the combiner means7 combine signals from the different transmitters before they areapplied to the antenna, and the branching means 8 apply the signalsreceived by the antenna to the receivers of the different channel units.The antenna, combiner means and branching means will be referred to asantenna means below.

The base station 13 shown in the FIGURE further comprises, in additionto the fixed channel units 1, 2 and 3, an additional channel unit 9, theantenna attachments of which can be connected by a switching means 10 tothe antenna means of sector 1, sector 2 or sector 3 so that the trafficcapacity of the additional channel unit is available to the concernedsector. The switching means 10 is a relay-type switch, the operation ofwhich is controlled by a control unit 11.

The control unit 11 monitors the operation of the fixed channel units 1,2 and 3 during the normal operation of the base station. The controlunit is connected to a base station controller (BSC) 12. If one of thechannel units fails, the control unit 11 connects the antennaattachments of the additional channel unit 9 by the switch 10 to thesector of the failed channel unit. This measure thus requires a singlecomponent, i.e. the relay-type (or semiconductor-type) switch 10.

As appears from the FIGURE, there is no connection between the antennaattachments of the channel units 1, 2 and 3, which ensures that if thereshould occur such a failure in one of the channel units that the antennaattachment of the channel unit would forward signals of a frequencywhich could interfere with the operation of the other channel units ofthe base station, these signals would not be able to propagate to theother channel units of the base station.

It is to be understood that the above description and the FIGURE relatedto it are only intended to illustrate a preferred embodiment of the basestation according to the invention without limiting the invention assuch. Accordingly, it is obvious that the number of base stationsectors, fixed channel units and additional channel units may differfrom the above example, and that the method and the base stationaccording to the invention can also be utilized in other systems thanthe GSM system, even though the invention has been described above byway of example with reference to the GSM system. The preferredembodiments of the method and the base station according to theinvention may vary within the scope of the attached claims.

We claim:
 1. A method for securing the operation of a base stationhaving a radio coverage area divided into at least two sectors, the basestation comprising individually for each said sector an antenna, acombiner arranged for combining signals transmitted by a plurality ofchannel units to be applied to the antenna, a brancher for branchingarranged signals received by the antenna to receivers of a plurality ofchannel units, and at least one channel unit assigned for each sector,each said assigned channel unit being arranged to be operativelyconnected by a respective combiner and a respective said brancher to arespective said antenna, collectively for enabling the base station toestablish radio connection with active radio transceivers currentlylocated in the respective sectors of the coverage area, wherein the basestation is provided with an additional channel unit having a trafficcapacity which is selectably switchable to any one or none of the basestation sectors, said method comprising:monitoring the operation of theassigned channel units of the base station; and switching, when one ofthe assigned channel units fails, the additional channel unit to thecombiner and brancher of the failed assigned channel unit by connectingantenna attachments of the additional channel unit thereto withoutthereby connecting said antenna attachments to an assigned channel unitfor another said sector.
 2. The method according to claim 1, wherein:theswitching is accomplished using a relay switch.
 3. The method accordingto claim 1, wherein:the base section is a base station in a cellularradio system.
 4. The method according to claim 1, wherein:the basestation is a base station in a GSM system.
 5. A base station in a radiosystem, and arranged to serve a radio coverage area which is dividedinto at least two sectors, said base station comprising:individually foreach said sector an antenna, a combiner arranged for combining signalstransmitted by a plurality of channel units to be applied to theantenna, a brancher arranged for branching signals received by theantenna to receivers of a plurality of channel units, and at least onechannel unit assigned for each sector, each said assigned channel unitbeing arranged to be operatively connected by a respective combiner anda respective said brancher to a respective said antenna, collectivelyfor enabling the base station to establish a radio connection withactive radio transceivers currently located in the respective sectors ofthe coverage area; an additional channel unit having a traffic capacitywhich is selectably switchable to any one or none of the base stationsectors; and a switch arranged for connecting the additional channelunit to the combiner and brancher of antenna attachments of theadditional channel unit without thereby connecting said antennaattachments to an assigned channel for another said sector.
 6. The basestation according to claim 5, further comprising:a control means, whichmonitors the operation of the assigned channel units, the control meansbeing arranged for controlling the switching means so that when anassigned channel unit fails, the control means connects the antennaattachments of the additional channel unit to the antenna means of thefailed assigned channel unit.
 7. The base station according to claim 5,wherein the switching means is a relay switch.
 8. The base stationaccording to claim 5, wherein the base station is a base stationcellular radio system.
 9. The base station according to claim 5, whereinthe base station is a GSM system base station.